P1618 Sensor Reference Voltage 1 Erratic

P1618 code - When the Powertrain Control Module (PCM) recognizes the primary 5-volt supply circuit voltage is verying too much too quickly. The MIL light illuminate and the ECT light will flash.

P1618

Possible causes P1618 code

- 5 volt supply circuit intermittent shorted to ground
- 5 volt supply circuit intermittent shorted to voltage
- 5 volt supply circuit intermittent open
- Crankshaft Position Sensor
- Engine oil pressure sensor
- Throttle body assembly
- Accelerator pedal position (APP) sensor
- Powertrain Control Module (PCM)

Diagnostic test P1618 code

Step 1. Check for an intermittent connection in the engine wiring harness
Diagnose any active or pending sensor reference high or sensor reference low DTCs before proceeding with this test procedure. If this DTC is present without an active or pending sensor reference high or sensor reference low DTC, the most likely cause in an intermittent open or short circuit in the wiring harness between the engine and the PCM.
Turn the ignition off, disconnect the throttle body assembly harness connector. Connect a voltmeter to the 5 volt supply circuit at the throttle body assembly harness connector.
Make sure that there is a good positive connection between the voltmeter lead and the throttle body assembly terminal since we are looking for an intermittent connection.
Turn the ignition on, while monitoring the voltage reading on the voltmeter, wiggle test the entire engine wiring harness all the way to the PCM. Look for any quick changes in the voltmeter reading. The voltmeter should read steady 5 volts +/- .01 or .02 volts with the throttle body assembly harness connector unplugged.

Did the voltmeter reading change from 5 volts at any time while wiggle testing the wiring?

Yes, repair the 5 volt supply circuit for an intermittent open or short  circuit in the wiring harness. Make sure to check all of the in-line connectors for poor connections or spread terminals.
No, go to step 2.

Step 2. Check for an intermittent connection in the APP wiring harness
Turn the ignition off, disconnect the APP sensor harness connector. Connect a voltmeter to the 5-volt supply circuit at the APP sensor harness connector. Turn the ignition on, while monitoring the voltage reading on the voltmeter, wiggle test the wiring harness between the APP sensor and the PCM.

Did the voltmeter reading change from 5.0 volts at any time while wiggle testing the wiring?

Yes, repair the 5 volt supply circuit for an intermittent open or short circuit in the wiring harness. Make sure to check all off the in-line connectors for poor connection or spread terminals.
No, go to step 3.

Step 3. Check the primary sensors
Turn the ignition off reconnect the throttle body harness connector. Reconnect the APP sensor harness connector, disconnect the PCM harness connector. Connect a voltmeter to the 5 volt supply circuit at the PCM harness connector. Turn the ignition on, while monitoring the voltage reading on the voltmeter, lightly tap on each sensor listed in the possible causes table.

Did the voltmeter reading change from 5.0 volts at any time while tapping on one of the sensors?

Yes, replace the sensor that caused the voltage to change.
No, go to step 4.

Step 4.  Check related PCM and component connections

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